1. Field of the Disclosure
The invention relates to determining the amount of carbon dioxide, and/or some other molecular species of gas, excreted during non-invasive ventilation.
2. Description of the Related Art
During invasive ventilation a sealed engagement is maintained between a respiratory circuit and the airway of the subject by an invasive interface appliance. For example, an endotracheal tube may maintain such a seal as pressurized gas is delivered to mechanically ventilate the subject. In such a configuration, determining excreted carbon dioxide or some other molecular species (e.g., to monitor gas exchange) may be fairly straightforward.
In non-invasive ventilation, pressurized gas causing mechanical ventilation is delivered to the airway of a subject via a non-invasive interface appliance. The non-invasive interface appliance interfaces in an unsealed manner with one or more external orifices of the airway of the subject. For example, a breathing mask forms a cavity that engages the face of the subject about the nose and mouth. Because non-invasive interface appliances allow for leakage of gas during respiration, accurate and/or precise detection of carbon dioxide may be more complicated (e.g., as excreted gas escapes through leaks).